More "semantic-versioning" compatible check for back-end schema

Summary

This MR refactors the checks for the mysql schema version.

Test Environment

Just put different values for MYSQL_SCHEMA_VERSION.

Check List for the Author

• All automated tests pass
• Reference related Issues
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.